The present invention relates to semi-invasive ultrasound imaging systems, and more particularly to transesophageal imaging systems and transnasal, transesophageal imaging systems that provide several two-dimensional plane views and projection views for visualizing three-dimensional anatomical structures inside a patient.
Non-invasive, semi-invasive and invasive ultrasound imaging has been widely used to view tissue structures within a human body, such as the heart structures, the abdominal organs, the fetus, and the vascular system. The semi-invasive systems include transesophageal imaging systems, and the invasive systems include intravascular imaging systems. Depending on the type and location of the tissue, different systems provide better access to or improved field of view of internal biological tissue.
In general, ultrasound imaging systems include a transducer array connected to a multiple channel transmit and receive beamformer. The transmit beamformer applies electrical pulses to the individual transducers in a predetermined timing sequence to generate transmit beams that propagate in predetermined directions from the array. As the transmit beams pass through the body, portions of the acoustic energy are reflected back to the transducer array from tissue structures having different acoustic characteristics. The receive transducers (which may be the transmit transducers operating in a receive mode) convert the reflected pressure pulses into corresponding electrical RF signals that are provided to the receive beamformer. Due to different distances from a reflecting point to the individual transducers, the reflected sound waves arrive at the individual transducers at different times, and thus the RF signals have different phases.
The receive beamformer has a plurality of processing channels with compensating delay elements connected to a summer. The receive beamformer selects the delay value for each channel to combine echoes reflected from a selected focal point. Consequently, when delayed signals are summed, a strong signal is produced from signals corresponding to this point. However, signals arriving from different points, corresponding to different times, have random phase relationships and thus destructively interfere. The receive beamformer selects such relative delays that control the orientation of the receive beam with respect to the transducer array. Thus, the receive beamformer can dynamically steer the receive beams to have desired orientations and can focus them at desired depths. The ultrasound system thereby acquires acoustic data.
To view tissue structures in real-time, various ultrasound systems have been used to generate two-dimensional or three-dimensional images. A typical ultrasound imaging system acquires a two-dimensional image plane that is perpendicular to the face of the transducer array applied to a patient""s body. To create a three-dimensional image, the ultrasound system must acquire acoustic data over a three-dimensional volume by, for example, moving a one-dimensional (or a one-and-half dimensional) transducer array over several locations. Alternatively, a two-dimensional transducer array can acquire scan data over a multiplicity of image planes. In each case, the system stores the image plane data for reconstruction of three-dimensional images. However, to image a moving organ, such as the heart, it is important to acquire the data quickly and to generate the images as fast as possible. This requires a high frame rate (i.e., the number of images generated per unit time) and fast processing of the image data. However, spatial scanning (for example, when moving a one-dimensional array over several locations) is not instantaneous. Thus, the time dimension is intertwined with the three space dimensions when imaging a moving organ.
Several ultrasound systems have been used to generate 3D images by data acquisition, volume reconstruction, and image visualization. A typical ultrasound system acquires data by scanning a patient""s target anatomy with a transducer probe and by receiving multiple frames of data. The system derives position and orientation indicators for each frame relative to a prior frame, a reference frame or a reference position. Then, the system uses the frame data and corresponding indicators for each frame as inputs for the volume reconstruction and image visualization processes. The 3D ultrasound system performs volume reconstruction by defining a reference coordinate system within which each image frame in a sequence of the registered image frames. The reference coordinate system is the coordinate system for a 3D volume encompassing all image planes to be used in generating a 3D image. The first image frame is used to define the reference coordinate system (and thus the 3D volume), uses either three spherical axes (rv, xe2x8ax96v and xcfx86v axes) or three orthogonal axes (i.e., xv, yv and zv axes). Each image frame is a 2D slice (i.e., a planar image) has two polar axes (i.e., ri and xe2x8ax96i axes) or two orthogonal axes (i.e., xi and yi), where i is the i-th image frame. Thus, each sample point within an image plane has image plane coordinates in the image plane coordinate system for such image plane. To register the samples in the reference coordinate system, the sample point coordinates in the appropriate image plane coordinate system are transposed to the reference coordinate system. If an image plane sample does not occur at specific integer coordinates of the reference coordinate system, the system performs interpolation to distribute the image plane sample among the nearest reference coordinate system points.
To store sample data or the interpolated values derived from the sample data, the system allocates memory address space, wherein the memory can be mapped to the reference coordinate system. Thus, values for a given row of a given reference volume slice (taken along, for example, the z-axis) can be stored in sequential address locations. Also, values for adjacent rows in such slice can be stored in adjacent first memory address space. The system performs incremental reconstruction by computing a transformation matrix that embodies six offsets. There are three offsets for computing the x, y, and z coordinates in the x-direction (along the row of the image), and three offsets for computing the x, y, and z coordinates in the y-direction (down the column of the image). Then, the system computes the corners of the reconstruction volume and compares them with the coordinates of the bounding volume. Next, the system determines the intersecting portion of the acquired image and the bounding coordinates and converts them back to the image""s coordinate system. This may be done using several digital signal processors.
Furthermore, the system can compute an orthogonal projection of the current state of the reconstruction volume. An orthogonal projection uses simpler computation for rendering (no interpolations need to be computed to transform from the reference coordinate system to a displayed image raster coordinate system). The system can use a maximum intensity projection (MIP) rendering scheme in which a ray is cast along the depth of the volume, and the maximum value encountered is the value that is projected for that ray (e.g., the value used to derive a pixel for a given raster point on the 2D image projection). The system incrementally reconstructs and displays a target volume in real time. The operator can view the target volume and scan effectiveness in real time and improve the displayed images by deliberately scanning desired areas repeatedly. The operator also can recommence volume reconstruction at the new viewing angle.
The image visualization process derives 2D image projections of the 3D volume over time to generate a rotating image or an image at a new viewing angle. The system uses a shear warp factorization process to derive the new 2D projection for a given one or more video frames of the image. For each change in viewing angle, the process factorizes the necessary viewing transformation matrix into a 3D shear which is parallel to slices of the volume data. A projection of the shear forms a 2D intermediate image. A 2D warp can be implemented to produce the final image, (i.e., a 2D projection of the 3D volume at a desired viewing angle). The system uses a sequence of final images at differing viewing angles to create a real-time rotating view of the target volume.
Other systems have been known to utilize power Doppler images alone in a three dimensional display to eliminate the substantial clutter caused by structural information signals. Such Doppler system stores Doppler power display values, with their spatial coordinates, in a sequence of planar images in an image sequence memory. A user can provide processing parameters that include the range of viewing angles. For instance, the user can input a range of viewing angles referenced to a line of view in a plane that is normal to the plane of the first image in the sequence, and a range increment. From these inputs the required number of three dimensional projections is computed. Then, this system forms the necessary sequence of maximum intensity projections by first recalling the planar Doppler power images from the image sequence memory for sequential processing by a scan converter and display processor. The processor rotates each planar image to one of the viewing angles projected back to the viewing plane.
The Doppler system accumulates the pixels of the projected planar images on a maximum intensity basis. Each projected planar image is overlaid over the previously accumulated projected images but in a transposed location in the image plane which is a function of the viewing angle and the interplane spacing: the greater the viewing angle, the greater the transposition displacement from one image to the next. The display pixels chosen from the accumulated images are the maximum intensity pixels taken at each point in the image planes from all of the overlaid pixels accumulated at each point in the image. This effectively presents the maximum intensity of Doppler power seen by the viewer along every viewing line between the viewer and the three dimensional representation.
This system can rotate, project, transpose, overlay, and choose the maximum intensities at each pixel for all of the planar images, and then store in the image sequence memory the resulting three dimensional representation for the viewing angle. The stored three dimensional sequence is available for recall and display upon command of the user. As the sequence is recalled and displayed in real time, the user can see a three dimensional presentation of the motion or fluid flow occurring in the volumetric region over which the planar images were acquired. The volumetric region is viewed three dimensionally as if the user were moving around the region and viewing the motion or flow from changing viewing angles. The viewer can sweep back and forth through the sequence, giving the impression of moving around the volumetric region in two directions.
It has also been known to utilize a modified two dimensional ultrasonic imaging system to provide three dimensional ultrasonic images. Such three dimensional ultrasonic imaging system can use conventional two dimensional ultrasonic imaging hardware and a scan converter. The two dimensional ultrasonic imaging system acquires a plurality of two dimensional images. This system processes the images through scan conversion to approximate their rotation to various image planes and projection back to a reference plane, which can be the original image plane. Conventional scan conversion hardware can be used to rescale the sector angle or depth of sector images, or the aspect ratio of rectangular images. This system projects a plurality of planes for each image and then stores them in a sequence of combined images, wherein each combined image comprises a set of corresponding projected images offset with respect to each other. Each combined image is a different view of a three dimensional region occupied by the planar image information.
The above system can replay the sequence of combined images on a display to depict the three dimensional region as if it is rotating in front of a viewer. Furthermore, the system can recall the stored combined images on the basis of the three dimensional viewing perspectives and displayed sequentially in a three dimensional presentation.
There are several medical procedures where ultrasound imaging systems are not yet widely used. Currently, for example, interventional cardiologists use mainly fluoroscopic imaging for guidance and placement of devices in the vasculature or in the heart. These procedures are usually performed in a cardiac catheterization laboratory (Cathlab) or an electrophysiology laboratory (Eplab). During cardiac catheterization, a fluoroscope uses X-rays on a real-time frame rate to give the physician a transmission view of a chest region, where the heart resides. A bi-plane fluoroscope, which has two transmitter-receiver pairs mounted at 90xc2x0 to each other, provides real-time transmission images of the cardiac anatomy. These images assist the physician in positioning various catheters by providing him (or her) with a sense of the three-dimensional geometry of the heart.
While fluoroscopy is a useful technique, it does not provide high quality images with good contrast in soft tissues. Furthermore, the physician and the assisting medical staff need to cover themselves with a lead suit and need to reduce the fluoroscopic imaging time whenever possible to lower their exposure to X-rays. In addition, fluoroscopy may not be available for some patients, for example, pregnant women, due to the harmful effects of the X-rays. Recently, transthoracic and transesophageal ultrasound imaging have been very useful in the clinical and surgical environments, but have not been widely used in the Cathlab or Eplab for patients undergoing interventional techniques.
Therefore there is a need for transesophageal or transnasal, transesophageal ultrasound systems and methods that can provide fast and computationally inexpensive real-time imaging. The images should enable effective visualization of the internal anatomy that includes various structures and provide selected views of the tissue of interest. An ultrasound system and method providing anatomically correct and easily understandable, real-time images would find additional applications in medicine.
The present invention relates to novel transesophageal ultrasound apparatuses or methods for imaging three-dimensional anatomical structures and/or medical devices (e.g., therapy devices, diagnostic devices, corrective devices, stents) introduced inside a patient.
According to one aspect, a transesophageal ultrasound imaging system for imaging biological tissue includes a transesophageal probe connected to a two-dimensional ultrasound transducer array, a transmit beamformer, a receive beamformer, and an image generator. The two-dimensional transducer array is disposed on a distal portion of the probe""s elongated body. The transmit beamformer is connected to the transducer array and is constructed to transmit several ultrasound beams over a selected pattern defined by azimuthal and elevation orientations. The receive beamformer is connected to the transducer array and is constructed to acquire ultrasound data from the echoes reflected over a selected tissue volume. The tissue volume is defined by the azimuthal and elevation orientations and a selected scan range. The receive beamformer is constructed to synthesize image data from the acquired ultrasound data. The image generator is constructed to receive the image data and generate images of the selected tissue volume that are displayed on an image display (a video display, a printer, etc.).
Preferred embodiments of this aspect include one or more of the following features:
The image generator is constructed to generate, from the image data, at least two orthographic projection views over the selected tissue volume, and the image display is constructed to display the at least two projection views.
The ultrasound imaging system may include a surface detector and a control processor. The surface detector is constructed to receive image parameters from the control processor and generate surface data from the image data. The image generator is constructed to generate from the surface data a projection image for display on the image display.
The surface detector is a B-scan boundary detector and the image generator is constructed to generate from the image data and the surface data a plane view including the projection image. Furthermore, the image generator may be constructed to generate, from the image data and the surface data, at least two orthographic projection views each including the plane view and the projection image. The surface detector may be a C-scan boundary detector and the image generator is then constructed to generate a C-scan view.
The ultrasound imaging system includes a probe that is a transesophageal probe or a transnasal transesophageal probe. The transesophageal probe includes a locking mechanism co-operatively arranged with an articulation region of the probe and constructed to lock in place the transducer array after orienting the array relative to a tissue region of interest. The transnasal transesophageal probe includes a locking mechanism co-operatively arranged with an articulation region of the probe and constructed to lock in place the transducer array after orienting the array relative to a tissue region of interest.
The transducer array and the beamformers are constructed to operate in a phased array mode and acquire the ultrasound data over the selected azimuthal range for several image sectors each having a designated elevation location. The transducer array includes a plurality of sub-arrays connected to the transmit and receive beamformers.
The image generator is constructed to generate, from the image data, at least two orthographic projection views over the selected tissue volume, and the image display is constructed to display the at least two projection views. The image generator is constructed to generate two of the orthographic projection views as orthogonal B-scan views and generate one of the orthographic projection views as a C-scan view.
The transesophageal probe may also include a locking mechanism co-operatively arranged with an articulation region of the probe and constructed to lock in place the transducer array after orienting the array relative to a tissue region of interest.
The ultrasound imaging system includes a control processor constructed and arranged to control the transmission of the ultrasound beams and control the synthesis of the image data based on range data provided by a user. The transducer array includes a plurality of sub-arrays connectable to the transmit and receive beamformers and the control processor is constructed to control arrangement of the sub-arrays for optimizing acquisition of the echo data of the tissue volume. The control processor constructed and arranged to provide to the transmit beamformer and the receive beamformer scan parameters that include an imaging depth, a frame rate, or an azimuth to elevation scan ratio.
The control processor is constructed to receive input data and provide output data causing the transmit and receive beamformers to change the azimuthal range. The control processor is constructed to receive input data and provide output data causing the transmit and receive beamformers to change the elevation range. The control processor is constructed to provide data to image generator for adjusting a yaw of the views by recalculating the orthographic projection views. By changing the azimuthal range or the elevation range, a clinician can direct the scan over a smaller data volume centered on the tissue of interest. By scanning over the smaller volume, the system improves real-time imaging of moving tissue by increasing the frame rate, because it collects a smaller number of data points.
The image generator includes at least one view interpolation processor constructed to generate the at least two orthographic projection views, at least one icon generator constructed to generate the at least two icons associated with the at least two orthographic projection views, and includes at least one boundary detector constructed and arranged to detect a tissue boundary.
The view interpolation processor is arranged to generate a B-scan view and a C-scan view, the C-scan view is generated by receiving C-scan designation information from the B-scan view. The view interpolation processor is an azimuthal view interpolation processor. The view interpolation processor is an elevation view interpolation processor. The view interpolation processor includes a gated peak detector.
The boundary detector is a B-scan boundary detector and the interpolation processor is further arranged to receive from the B-scan boundary detector data for highlighting borders in the orthographic projection views. The boundary detector is a C-scan boundary detector and the interpolation processor is further arranged to receive from the C-scan boundary detector data for highlighting borders in the orthographic projection views.
The image generator includes a yaw adjustment processor. The image generator includes a range processor constructed to provide two range cursors for generating a C-scan projection view. The range processor is arranged to receive a user input defining the two range cursors. The icon generator constructed to generate an azimuthal icon displaying the azimuthal angular range and displaying a maximum azimuthal angular range. The icon generator constructed to generate an elevation icon displaying the elevation angular range and displaying a maximum elevation angular range.
According to another aspect, a transesophageal ultrasound imaging method is performed by introducing into the esophagus a transesophageal probe and positioning a two-dimensional ultrasound transducer array at a selected orientation relative to an tissue region of interest, transmitting ultrasound beams over a plurality of transmit scan lines from the transducer array over a selected azimuthal range and a selected elevation range of locations, and acquiring by the transducer array ultrasound data from echoes reflected from a selected tissue volume delineated by the azimuthal range, the elevation range and a selected sector scan depth and synthesizing image data from the acquired ultrasound data. Next, the ultrasound imaging method is performed by generating images from the image data of the selected tissue volume, and displaying the generated images.
Preferably, the transesophageal ultrasound imaging method may be performed by one or more of the following: The transmitting and the acquiring is performed by transmit and receive beamformers constructed to operate in a phased array mode and acquire the ultrasound data over the selected azimuthal range for several image sectors having known elevation locations. The generating includes generating at least two orthographic projection views over the tissue volume, and the displaying includes displaying at least two orthographic projection views.
The imaging method may be used for positioning a surgical instrument at a tissue of interest displayed by the orthographic projection views. The imaging method may be used for verifying a location of the surgical instrument during surgery based orthographic projection views. The imaging method may be used for performing the transmitting, the acquiring, the generating, and the displaying of the orthographic projection views while performing surgery with the surgical instrument. The imaging method may be used for performing the transmitting, the acquiring, the generating, and the displaying of the orthographic projection views after performing surgery with the surgical instrument.
The generation of at least two orthographic projection views may include generating a selected C-scan view. The generation of the selected C-scan view may include providing a C-scan designation for the selected C-scan view. The designation may include defining a bottom view or defining a top view. The generation of the C-scan may include detecting a tissue boundary by using a C-scan boundary detector, and selecting ultrasound data for the C-scan by a gated peak detector.
The imaging method may include providing input data to a control processor and providing output data from the control processor to direct the transmit and receive beamformers to change the azimuthal range. The imaging method may include providing input data to a control processor and providing output data from the control processor to direct the transmit and receive beamformers to change the elevation range. The control processor may also provide data to image generator for adjusting a yaw of the views by recalculating the orthographic projection views. By changing the azimuthal range or the elevation range, a clinician can direct the scan over a smaller data volume centered on the tissue of interest. By scanning over the smaller volume, the system improves real-time imaging of moving tissue by increasing the frame rate, because it collects a smaller number of data points.
The generation of at least two orthographic projection views may include generating an azimuthal icon associated with the selected azimuthal range and a maximum azimuthal range, or an elevation icon associated with the selected elevation range and a maximum elevation range.